168 research outputs found
Observation of anomalous Hanle spin precession lineshapes resulting from interaction with localized states
It has been shown recently that in spin precession experiments, the
interaction of spins with localized states can change the response to a
magnetic field, leading to a modified, effective spin relaxation time and
precession frequency. Here, we show that also the shape of the Hanle curve can
change, so that it cannot be fitted with the solutions of the conventional
Bloch equation. We present experimental data that shows such an effect arising
at low temperatures in epitaxial graphene on silicon carbide with localized
states in the carbon buffer layer. We compare the strength of the effect
between materials with different growth methods, epitaxial growth by
sublimation and by chemical vapor deposition. The presented analysis gives
information about the density of localized states and their coupling to the
graphene states, which is inaccessible by charge transport measurements and can
be applied to any spin transport channel that is coupled to localized states.Comment: 6 pages, 6 figure
Magnetotransport in graphene on silicon side of SiC
We have studied the transport properties of graphene grown on silicon side of
SiC. Samples under study have been prepared by two different growth methods in
two different laboratories. Magnetoresistance and Hall resistance have been
measured at temperatures between 4 and 100 K in resistive magnet in magnetic
fields up to 22 T. In spite of differences in sample preparation, the field
dependence of resistances measured on both sets of samples exhibits two periods
of magneto-oscillations indicating two different parallel conducting channels
with different concentrations of carriers. The semi-quantitative agreement with
the model calculation allows for conclusion that channels are formed by
high-density and low-density Dirac carriers. The coexistence of two different
groups of carriers on the silicon side of SiC was not reported before.Comment: 5 pages, 6 figures, accepted for publication in the "IOP Journal of
Physics: Conference series" as a contribution to the proceedings of the 20th
International Conference on "High Magnetic Fields in Semiconductor Physics",
HMF 2
Integrated AlGaN quadruple-band ultraviolet photodetectors
Cataloged from PDF version of article.Monolithically integrated quadruple back-illuminated ultraviolet metalsemiconductormetal photodetectors with four different spectral responsivity bands were demonstrated on each of two different Al xGa 1-xN heterostructures. The average of the full-width at half-maximum (FWHM) of the quantum efficiency peaks was 18.15nm for sample A, which incorporated five 1000nm thick epitaxial layers. In comparison, the average FWHM for sample B was 9.98 nm, which incorporated nine 500nm thick epitaxial layers. © 2012 IOP Publishing Ltd
Patterning of graphene on silicon-on-insulator waveguides through laser ablation and plasma etching
We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to be 0.132 dB/μm
Bilayer graphene inclusions in rotational-stacked multilayer epitaxial graphene
Additional component in multi-layer epitaxial graphene grown on the
C-terminated surface of SiC, which exhibits the characteristic electronic
properties of a AB-stacked graphene bilayer, is identified in magneto-optical
response of this material. We show that these inclusions represent a
well-defined platform for accurate magneto-spectroscopy of unperturbed graphene
bilayers.Comment: 5 pages, 2 figures, to appear in Phys. Rev.
Effect of growth pressure on coalescence thickness and crystal quality of GaN deposited on 4H-SiC
Cataloged from PDF version of article.The influence of growth pressure on the coalescence thickness and the crystal quality of GaN deposited on 4H-SiC by low pressure metalorganic vapor phase epitaxy was studied. It was shown that growth pressure has an impact on the surface roughness of epilayers and their crystal quality. GaN coalescence thicknesses were determined for the investigated growth pressures. The GaN layers were characterized by AFM and HRXRD measurements. HEMT structures were also fabricated and characterized. Among the growth pressures studied, 50, 125 and 200 mbar, 200 mbar was found to be most suitable for GaN/SiC epitaxy. (C) 2010 Elsevier B.V. All rights reserved
- …